mb/purism/librem_cnl: Add ramtop to cmos.layout for librem_mini

Since commit e633d370 (soc/intel/cometlake: Enable early caching of
RAMTOP region), cmos.layout for Cannon Lake boards must have a ramtop
entry, add it.

Change-Id: I2bf71f2dd79f2e1e2e13f62a3e08103336bbad61
Signed-off-by: Jonathon Hall <jonathon.hall@puri.sm>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/77670
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/purism/librem_cnl/variants/librem_mini/cmos.layout

@@ -4,6 +4,7 @@ entries
 
 # start-bit	length	config	config-ID	name
 0		112	r	0		reserved_memory
+400		80	r	0		ramtop
 1352		8	e	1		power_on_after_fail
 
 enumerations